Low bit rate video encoding suppresses high frequency components and minimizes motion compensation residuals. This results in a grid like blocky appearance of the decoded image. Sharp transitions in encoding parameters at block boundaries are responsible for these blocky artifacts. Additionally at medium bitrates, a loss of high frequency components produces a shimmering effect (called ringing) at high contrast edges. Low pass filtering can rectify these artifacts.
De-blocking filters eliminate or minimize the blockiness by blurring the block boundaries. A low pass filter blur can merge the block boundaries into their surrounding blocks making the transition smoother and eliminating the blocky look. However indiscriminate low pass edge filtering can cause a loss of contrast especially when high frequency image objects are located at or close to block boundaries.
Further limitations and disadvantages of conventional and traditional approaches will become apparent to one of skill in the art, through comparison of such systems with embodiments of the present invention as set forth in the remainder of the present application with reference to the drawings.